Herbicidal tetrahydrofuran derivatives

ABSTRACT

Certain benzyloxymethyltetrahydrofuran derivatives are useful as herbicides.

The present invention relates to novel tetrahydrofuran derivatives to bespecified hereinafter, as well as to a method of their preparation. Thetetrahydrofuran derivatives according to the present invention haveinteresting herbicidal properties. The present invention therefore alsorelates to herbicidal compositions comprising a carrier or asurface-active agent or both a carrier and a surface-active agent and atleast one tetrahydrofuran derivative to be specified hereinafter. Thepresent invention also relates to a method of eradicating or controllingweeds infesting cereal crops at a locus by applying a herbicidallyeffective amount of a tetrahydrofuran derivative or a compositioncontaining a tetrahydrofuran derivative according to the presentinvention.

The novel compounds according to the present invention aretetrahydrofuran derivatives of the general formula: ##STR1## wherein R¹and R² each individually represents a hydrogen atom, a halogen atom, anoptionally substituted alkyl, cycloalkyl or aryl group or R¹ and R²together represent an alkylene moiety, R³, R⁴, R⁵ and R⁶ eachindividually represents a hydrogen atom, a halogen atom having an atomicnumber of from 9 to 35, inclusive, an optionally substituted alkyl,alkoxy, thioalkoxy or aryl group or one of R³ and R⁴ and one of R⁵ andR⁶ together represent a carbon-carbon bond or an epoxide moiety; R⁷represents a hydrogen atom or optionally substituted alkyl group; R⁸ andR⁹ each individually represents a hydrogen atom or an optionallysubstituted alkyl group; and Ar represents an optionally substitutedphenyl group.

Preferred tetrahydrofuran derivatives are those of formula I, wherein R¹and R² each individually represents a hydrogen atom, an alkyl group ofup to 6 carbon atoms or a substituted or unsubstituted phenyl group; ortogether represent an alkylene moiety of up to 6 carbon atoms; R³, R⁴,R⁵ and R⁶ each individually represents a hydrogen atom, a halogen atomor an alkyl group of up to 6 carbon atoms or one of R³ and R⁴ and one ofR⁵ and R⁶ together represent a carbon-carbon bond; R⁷ represents ahydrogen atom or an alkyl group of up to 6 carbon atoms; R⁸ and R⁹ eachindividually represents a hydrogen atom or an alkyl group of up to 6carbon atoms; and Ar represents a phenyl group or a phenyl groupsubstituted by one or more halogen atoms or alkyl or alkoxy groups of upto 6 carbon atoms.

Particularly preferred tetrahydrofuran derivatives are those of formulaI, wherein R¹ and R² each individually represents a hydrogen atom, amethyl group, or R¹ and R² together represent a pentamethylene moiety;R³, R⁴, R⁵ and R⁶ each individually represents a hydrogen atom or one ofR³ and R⁴ and one of R⁵ and R⁶ together represent a carbon-carbon bond;R⁷ represents a hydrogen atom, a methyl or ethyl group, preferably anethyl group; R⁸ and R⁹ each individually represents a hydrogen atom; andAr represents a phenyl group or a phenyl group substituted with a2-methyl-, 2-fluoro- or a 2,6-dichloro group.

Suitable substituents referred to hereinabove comprise halogen atomshaving an atom number of from 9 to 35, inclusive, especially chlorine orfluorine atoms; and alkyl, alkoxy or thioalkoxy group, the alkylportions of which each contain from 1 to 6 carbon atoms, an aryl oraryloxy group, the aryl portions of which each contain from 6 to 12carbon atoms, preferably a phenyl group, or a cycloalkyl groupcontaining 3 to 6 carbon atoms.

The tetrahydrofuran derivatives according to the present invention canexist in several geometric forms, such as cis-configuration,trans-configuration as well as in optically active forms. These forms aswell as mixtures thereof are within the scope of the present invention.The various isomers of the tetrahydrofuran derivatives of formula I mayhave different herbicidal activities. Thus, one may prefer to resolve anisomer mixture to recover a more herbicidally active isomer or toprepare the more active form for use in the invention.

The tetrahydrofuran derivatives according to the present invention maybe prepared by reacting a compound of formula: ##STR2## with a compoundof formula: ##STR3## wherein R¹ -R⁹ and Ar have the meanings as definedhereinbefore and one of X and Y represents a halogen atom and the othera group OZ, wherein Z represents a hydrogen atom or an alkali oralkaline earth atom.

The reaction is preferably carried out by reacting a compound of formulaII, wherein Y represents a hydroxy group with a compound of formula III,wherein X represents a halogen atom in the presence of a base, such assodium hydride, if desired in the presence of an aromatic solvent, suchas benzene or toluene. The reactions are suitably carried out underreflux conditions.

The compounds of formula II can be prepared by methods known in the art.

As mentioned hereinbefore, the tetrahydrofuran derivatives according tothe present invention are of interest as herbicides. The inventiontherefore includes herbicidal compositions comprising a carrier and/or asurface-active agent together with at least one tetrahydrofuranderivative according to formula I. The present invention also includes amethod of eradicating or controlling weeds in crops at a locus byapplying to a locus a herbicidally active amount of a tetrahydrofuranderivative according to formula I or a composition containing as activeingredient at least one tetrahydrofuran derivative according to formulaI.

The term "carrier" as used herein means a solid or fluid material withwhich the active ingredient is mixed or formulated to facilitate itsapplication to the plant, seed, soil or other object to be treated, orits storage, transport or handling. Any of the carrier materials orsurface-active agents usually applied in formulating pesticides may beused in the compositions according to the invention, and suitableexamples of these are to be found, for example, in British patentSpecification No. 1,293,546.

The compositions of the invention may be formulated as wettable powders,dusts, granules, solutions, emulsifiable concentrates, emulsions,suspensions, concentrates or aerosols. Wettable powders are usuallycompounded to contain 25-75% w of toxicant and usually contain, inaddition to solid carrier, 3-10% w of a dispersing agent and, wherenecessary, up to 10% w of stabilizer(s) and/or additives such aspenetrants or stickers. Dusts are usually formulated as a dustconcentrate having a similar composition to that of a wettable powderbut without a dispersant, and are diluted in the field with furthersolid carrier to give a composition usually containing 0.5-10% w oftoxicant. Granules are usually prepared to have a size between 0.15 and1.68 mm, and may be manufactured by agglomeration or impregnationtechniques. Generally, granules will contain 0.5-25% w of toxicant and,where necessary, up to 10% w of additives, such as stabilizers,slow-release modifiers and binding agents. Emulsifiable concentratesusually contain, in addition to the solvent and, where necessary,co-solvent, 10-50% w/v of toxicant, 2-20% w/v of emulsifiers and, wherenecessary, up to 20% w/v of appropriate additives, such as stabilizers,penetrants and corrosion inhibitors. Suspension concentrates arecompounded so as to obtain a stable, non-sedimenting, flowable productand usually contain 10-75% w of toxicant, 0.5-15% w of dispersingagent(s), 0.1-10% w of suspending agents, such as protective colloidsand thioxotropic agents, and, where necessary, up to 10% w ofappropriate additives, such as defoamers, corrosion inhibitors,stabilizers, penetrants and stickers, and as carrier, water or anorganic liquid in which the toxicant is substantially insoluble; certainorganic solids or inorganic salts may be dissolved in the carrier toassist in preventing sedimentation or as anti-freeze agents for water.

Aqueous dispersions and emulsions, for example compositions obtained bydiluting a wettable powder or an emulsifiable concentrate according tothe invention with water, also lie within the scope of the presentinvention. The said emulsions may be of the water-in-oil or theoil-in-water type, and may have a thick `mayonaise`-like consistency.

The compositions according to the invention may also contain otheringredients, for example those mentioned in British patent SpecificationNo. 1,293,546, and/or other pesticidally active compounds, such asinsecticides, acaricides, herbicides or fungicides which are compatiblewith the other ingredients in the composition.

The invention is further illustrated in the following Examples. Thestructures of the compounds prepared were confirmed by elemental andN.M.R. analysis.

EXAMPLE 1 Preparation of 2,5,5-trimethyl-2-(2-methylbenzyloxymethyl)tetrahydrofuran

2,5,5-Trimethyl-2-hydroxymethyl tetrahydrofuran (1.6 g) was added slowlyto a stirred suspension of sodium hydride (0.4 g of 80% dispersion inoil) in dry toluene (55 ml). After the addition the mixture was heatedunder reflux for 1 hour. 2-Methylbenzyl chloride (1.8 g) was added andthe mixture heated under reflux overnight. The cooled mixture was washedwith water (x2) and dried and the solvent was removed under reducedpressure. The product was purified by chromatography on silica usingmethylene dichloride as eluent. Yield 80%.

Analysis: Calculated for C₁₆ H₂₄ O₂ : C, 77.4; H, 9.7%. Found: C, 77.1;H, 10.1%.

EXAMPLE 2 Preparation of 2,5,5-trimethyl-2-benzyloxymethyltetrahydrofuran

Hydrogen was added to a solution of2,5,5-trimethyl-2-benzyloxymethyldihydrofuran (4.7 g) in ethanol (100ml) under vigorous stirring in the presence of 5% Pd/(BaSO₄) at roomtemperature for 6 hours. After filtration the solvent was removed andthe product was purified by chromatography on silica usingacetone/petrol as eluent. Yield 57%.

Analysis: Calculated for C₁₅ H₂₂ O₂ : C, 76.0; H, 9.4%. Found: C, 77.2;H, 9.5%.

EXAMPLES 3-23

Further compounds were prepared whose physical characteristics andanalyses are set out in Table I.

EXAMPLE 24 Herbicidal activity

To evaluate their herbicidal activity, the compounds according to theinvention were tested using as a representative range of plants:--maize,Zea mays (Mz); rice, Oryza sativa (R); barnyard grass, Echinochloacrusgalli (BG); oat, Avena sativa (O); linseed, Linum usitatissimum (L);mustard, Sinapsis alba (M); sugar beet, Beta vulgaris (SB) and soyabean, Glycine max (S).

The tests fall into two categories, pre-emergence and post-emergence.The pre-emergence tests involved spraying a liquid formulation of thecompound onto the soil in which the seeds of the plant species mentionedabove had recently been sown. The post-emergence tests involved twotypes of test, viz., soil drench and foliar spray tests. In the soildrench tests the soil in which seedling plants of the above species weregrowing, was drenched with a liquid formulation containing a compound ofthe invention, and in the foliar spray tests the seedling plants weresprayed with such a formulation.

                                      TABLE I                                     __________________________________________________________________________    Ex-                                                                           ample                                                                             Compound            Analysis (%)                                          __________________________________________________________________________    3   2,5-dimethyl-2-benzyloxymethyl                                                                    Calculated for C.sub.14 H.sub.20 O.sub.2 : C                                  76.5; H 9.1                                               tetrahydrofuran     Found: C 76.0; H 9.2                                  4   2-benzyloxymethyl-5-phenyl                                                                        Calculated for C.sub.18 H.sub.20 O.sub.2 : C                                  80.6; H 7.5                                               tetrahydrofuran     Found: C 81.0; H 7.5                                  5   2,5,5-trimethyl-2-benzyloxymethyl                                                                 Calculated for C.sub.15 H.sub.20 O.sub.2 : C                                  77.6; H 8.6                                               dihydrofuran        Found: C 75.5; H 9.1                                  6   2,5,5-trimethyl-2-(2,6-dichloro-                                                                  Calculated for C.sub.15 H.sub.20 Cl.sub.2 O.sub.2                             : C 59.4; H 6.6                                           benzyloxymethyl) tetrahydrofuran                                                                  Found: C 59.8; H 6.7                                  7   2,5,5-trimethyl-2-(2-fluorobenzyl-                                                                Calculated for C.sub.15 H.sub.21 FO.sub.2 : C                                 71.4; H 8.3                                               oxymethyl) tetrahydrofuran                                                                        Found: C 71.7; H 8.6                                  8   2-methyl-2-benzyloxymethyl-dihydro-                                                               Calculated for C.sub.18 H.sub.24 O.sub.2 : C                                  79.4; H 8.8                                               furan-5-spirocyclohexane                                                                          Found: C 79.4; H 9.1                                  9   2-methyl-2-benzyloxymethyl-tetra-                                                                 Calculated for C.sub.18 H.sub.26 O.sub.2 : C                                  78.8; H 9.5                                               hydrofuran-5-spirocyclohexane                                                                     Found: C 79.1; H 9.5                                  10  2-methyl-2-(2-methylbenzyloxymethyl)-                                                             Calculated for C.sub.19 H.sub.28 O.sub.2 : C                                  79.2; H 9.7                                               tetrahydrofuran-5-spirocyclohexane                                                                Found: C 79.0; H 9.9                                  11  2-methyl-2-(2-fluorobenzyloxymethyl)-                                                             Calculated for C.sub.18 H.sub.25 FO.sub.2 : C                                 74.0; H 8.6                                               tetrahydrofuran-5-spirocyclohexane                                                                Found: C 74.2; H 8.6                                  12  2-methyl-2-(2,6-dichlorobenzyloxy-                                                                Calculated for C.sub.18 H.sub.24 Cl.sub.2 O.sub.2                             : C 63.0; H 7.0                                           methyl)-tetrahydrofuran-5-spiro-                                                                  Found: C 63.2; H 7.2                                      cyclohexane                                                               13  2,5,5-trimethyl-2-benzyloxymethyl-                                                                Calculated for C.sub.15 H.sub.20 O.sub.3 : C                                  72.6; H 8.1                                               3,4-epoxy tetrahydrofuran                                                                         Found: C 73.4; H 8.4                                  14  2-ethyl-5,5-dimethyl-2-benzyloxy-                                                                 Calculated for C.sub.16 H.sub.22 O.sub.2 : C                                  78.0; H 8.9                                               methyl dihydrofuran Found: C 78.1; H 9.5                                  15  2-ethyl-5,5-dimethyl-2-benzyloxy-                                                                 Calculated for C.sub.16 H.sub.24 O.sub.2 : C                                  77.4; H 9.7                                               methyl tetrahydrofuran                                                                            Found: C 77.1; H 10.1                                 16  2-ethyl-5,5-dimethyl-2-(2,6-dichloro-                                                             Calculated for C.sub.16 H.sub.22 Cl.sub.2 O.sub.2                             : C 60.6; H 6.9; Cl 22.4                                  benzyloxymethyl) tetrahydrofuran                                                                  Found: C 61.3; H 7.4; Cl 22.2                         17  2-ethyl-2-benzyloxymethyl-dihydro-                                                                Calculated for C.sub.19 H.sub.26 O.sub.2 : C                                  79.7; H 9.1                                               furan-5-spirocyclohexane                                                                          Found: C 79.9; H 9.3                                  18  2-ethyl-2-(2-fluorobenzyloxymethyl)-                                                              Calculated for C.sub.19 H.sub.27 O.sub.2 F: C                                 74.5; H 8.8                                               tetrahydrofuran-5-spirocyclohexane                                                                Found: C 79.9; H 9.3                                  19  2-ethyl-2-benzyloxymethyl-tetra-                                                                  Calculated for C.sub.19 H.sub.28 O.sub.2 : C                                  79.2; H 9.7                                               hydrofuran-5-spirocyclohexane                                                                     Found: C 79.2; H 10.0                                 20  2-ethyl-2-(2-methylbenzyloxymethyl)-                                                              Calculated for C.sub.20 H.sub.30 O.sub.2 : C                                  79.5; H 9.9                                               tetrahydrofuran-5-spirocyclohexane                                                                Found: C 79.3; H 10.2                                 21  2-ethyl-2-(2,6-dichlorobenzyloxy-                                                                 Calculated for C.sub.19 H.sub.26 O.sub.2 Cl.sub.2                             : C 63.9; H 7.3                                           methyl)-tetrahydrofuran-5-spiro-                                                                  Found: C 64.4; H 7.7                                      cyclohexane                                                               22  2-ethyl-2-(2-bromobenzyloxymethyl)-                                                               Calculated for C.sub.19 H.sub.27 O.sub.2 Br: C                                62.1; H 7.4                                               tetrahydrofuran-5-spirocyclohexane                                                                Found: C 62.1; H 7.6                                  23  2,5,5-trimethyl-4-ethyl-2-benzyloxy-                                                              Calculated for C.sub.17 H.sub.26 O.sub.2 : C                                  77.9; H 9.9                                               methyl tetrahydrofuran                                                                            Found: C 77.6; H 10.3                                 __________________________________________________________________________

The soil used in the tests was a steam-sterilized, modified John InnesCompost mixture in which half the peat, by loose bulk, had been replacedby vermiculite.

The formulations used in the tests were prepared by diluting with waterand solutions of the compounds in acetone containing 0.4% by weight ofan alkylphenol/ethylene oxide condensate available under the trade nameTRITON X-155. In the soil spray and foliar spray tests the acetonesolutions were diluted with an equal volume of water and the resultingformulations applied at two dosage levels corresponding to 5 and 1kilogram(s) of active material per hectare respectively in a volumeequivalent to 400 liters per hectare. In the soil drench tests onevolume of the acetone solution was diluted to 155 volumes with water andthe resulting formulation applied at one dosage level equivalent to 10kilograms of active material per hectare in a volume equivalent toapproximately 3,000 liters per hectare.

In the pre-emergence tests untreated sown soil and in the post-emergencetests untreated soil bearing seedlings plants were used as controls.

The herbicidal effects of the compounds were assessed visually sevendays after spraying the foliage and drenching the soil and eleven daysafter spraying the foliage and drenching the soil and eleven days afterspraying the soil, and were recorded on a 0-9 scale. A rating 0indicates no effect on the treated plants, a rating 2 indicates areduction in fresh weight of stem and leaf of the plants ofapproximately 25%, a rating 5 indicates a reduction of approximately55%, a rating 9 indicates a reduction of 95%, etc.

The results of the tests are set out in Table II below.

                                      TABLE II                                    __________________________________________________________________________                       Post emergence (plants)                                                   Dose                                                                              Soil drench       Foliar spray                             Compound       kg/ha                                                                             Mz R BG O L M SB                                                                              S Mz R BG O L M SB                                                                              S                        __________________________________________________________________________    2,5,5-trimethyl-2-(2-                                                                        5   8  8 8  8 0 5 0 5 5  0 5  7 6 6 5 4                        .Iadd.methyl.Iaddend.benzyloxymethyl)                                         tetrahydrofuran                                                                              1                     0  0 2  4 3 3 1 1                        2,5,5-trimethyl-2-                                                                           5   8  7 8  8 6 4 5 5 7  3 9  7 6 6 5 6                        benzyloxymethyl                                                               tetrahydrofuran                                                                              1                     4  0 7  5 4 0 2 0                        2,5-dimethyl-2-                                                                              5   7  6 7  0 5 2 5 0 5  1 8  5 5 0 2 0                        benzyloxymethyl                                                               tetrahydrofuran                                                                              1                     0  0 0  0 0 0 0 0                        2-benzyloxymethyl-                                                                           5   6  5 7  0 0 0 0 0 4  0 7  0 8 7 6 5                        5-phenyl-tetra-                                                               hydrofuran     1                     0  0 2  0 5 1 0 2                        2,5,5-trimethyl-2-                                                                           5   8  7 8  6 7 6 5 1 6  0 8  4 4 4 5 4                        benzyloxymethyl                                                               dihydrofuran   1                     2  0 7  0 0 0 0 0                        2,5,5-trimethyl-2-                                                                           5   8  3 7  8 0 3 7 3 7  0 8  8 5 7 6 5                        (2,6-dichlorobenzyl-                                                          oxymethyl)tetra-                                                                             1                     2  0 2  2 0 4 4 2                        hydrofuran                                                                    2,5,5-trimethyl-2-(2-                                                                        5   9  7 9  8 6 7 3 6 4  0 3  4 0 5 3 2                        fluorobenzyloxymethyl)-                                                       tetrahydrofuran                                                                              1                     0  0 0  0 0 0 0 1                        2-methyl-2-benzyloxymethyl-                                                                  5   8  5 7  2 0 2 0 0 3  2 8  5 7 8 5 5                        dihydrofuran-5-spiro-                                                         cyclohexane    1                     1  0 1  0 5 3 0 2                        2-methyl-2-benzyloxy-                                                                        5   8  6 9  8 4 7 4 2 6  2 8  8 8 9 8 6                        methyl-tetrahydrofuran-                                                       5-spirocyclohexane                                                                           1                     5  0 6  5 6 6 3 4                        2-methyl-2-(2-methyl-                                                                        5   8  4 8  7 3 3 5 2 6  4 9  8 8 8 6 5                        benzyloxymethyl)-tetra-                                                       hydrofuran-5-spiro-                                                                          1                     3  0 7  5 7 7 1 3                        cyclohexane                                                                   2-methyl-2-(2-fluoro-                                                                        5   7  2 9  6 2 0 4 4 7  0 9  8 8 8 8 8                        benzyloxymethyl)-tetra-                                                       hydrofuran-5-spiro-                                                                          1                     4  0 8  3 8 5 5 5                        cyclohexane                                                                   2-methyl-2-(2,6-dichloro-                                                                    5   5  0 7  0 0 0 0 2 7  0 8  7 7 8 8 7                        benzyloxymethyl)-tetra-                                                       hydrofuran-5-spiro-                                                                          1                     2  0 7  5 7 7 7 6                        cyclohexane                                                                   2,5,5-trimethyl-2-benzyl-                                                                    5   7  4 7  7 2 3 4 0 4  0 7  0 0 5 2 5                        oxymethyl-3,4-epoxy-                                                          tetrahydrofuran                                                                              1                     0  0 4  0 0 3 0 3                        2-ethyl-5,5-dimethyl-2-                                                                      5   9  7 9  6 5 5 5 6 9  4 9  5 6 7 6 5                        benzyloxymethyl-dihydro-                                                      furan          1                     8  0 8  0 1 2 5 2                        2-ethyl-5,5-dimethyl-2-                                                                      5   9  8 9  8 6 6 7 6 9  8 9  8 7 7 8 7                        benzyloxymethyl-tetra-                                                        hydrofuran     1                     8  2 9  4 2 4 2 4                        2-ethyl-5,5-dimethyl-2-                                                                      5   9  6 9  8 0 0 7 3 9  5 9  8 8 7 7 7                        (2,6-dichlorobenzyloxy-                                                       methyl)-tetrahydrofuran                                                                      1                     8  2 8  6 7 5 5 6                        2-ethyl-2-benzyloxy-                                                                         5   8  6 9  6 0 3 0 0 8  3 9  8 7 7 6 7                        methyl-dihydrofuran-                                                          5-spirocyclohexane                                                                           1                     6  0 8  0 5 5 2 3                        2-ethyl-2-(2-fluorobenzyl-                                                                   5   8  5 9  7 3 0 0 0                                          oxymethyl)-tetrahydro-                                                        furan-5-spirocyclohexane                                                                     1                     5  0 9  6 7 6 0 3                        2-ethyl-2-benzyloxymethyl-                                                                   5   7  6 9  8 4 5 5 2 7  5 9  8 7 7 3 7                        tetrahydrofuran-5-spiro-                                                      cyclohexane    1                     6  1 8  5 6 5 0 2                        2-ethyl-2-(2-methylbenzyl-                                                                   5   6  0 9  8 2 3 4 1 7  4 8  7 6 6 2 6                        oxymethyl)-tetrahydro-                                                        furan-5-spirocyclohexane                                                                     1                     4  2 7  5 6 5 0 3                        2-ethyl-2-(2,6-dichloro-                                                                     5   3  0 8  5 0 0 2 0 5  1 8  6 6 7 0 6                        benzyloxymethyl)-tetra-                                                       hydrofuran-5-spiro-                                                                          1                     3  0 5  3 6 6 0 4                        cyclohexane                                                                   2-ethyl-2-(2-bromobenzyl-                                                                    5   4  0 7  6 0 0 0 0 8  0 8  8 7 7 2 5                        oxymethyl)-tetrahydro-                                                        furan-5-spirocyclohexane                                                                     1                     4  0 8  4 7 7 0 4                        2,5,5-trimethyl-4-ethyl-                                                                     5   8  5 9  8 0 3 6 0 6  0 9  7 5 5 3 3                        2-benzyloxymethyl-tetra-                                                      hydrofuran     1                     4  0 6  1 1 0 0 2                        __________________________________________________________________________                                         Seeds                                                                     Dose                                                                              Pre-emergence                                              Compound       kg/ha                                                                             Mz R BG O L M SB                                                                              S                        __________________________________________________________________________                      2,5,5-trimethyl-2-(2-                                                                        5   8  9 9  8 0 5 2 7                                          .Iadd.methyl.Iaddend.benzyloxymethyl)                                         tetrahydrofuran                                                                              1   5  8 9  4 0 0 0 2                                          2,5,5-trimethyl-2-                                                                           5   8  9 9  9 4 5 0 3                                          benzyloxymethyl                                                               tetrahydrofuran                                                                              1   7  9 9  8 0 3 0 2                                          2,5-dimethyl-2-                                                                              5   6  9 9  8 8 8 7                                            benzyloxymethyl                                                               tetrahydrofuran                                                                              1   0  6 8  0 8 4 0                                            2-benzyloxymethyl-                                                                           5   5  7 9  3 4 2 5 0                                          5-phenyl-tetra-                                                               hydrofuran     1   5  2 9  1 4 1 1 0                                          2,5,5-trimethyl-2-                                                                           5   8  9 9  9 6 3 4 1                                          benzyloxymethyl                                                               dihydrofuran   1   3  8 9  6 0 0 2 0                                          2,5,5-trimethyl-2-                                                                           5   9  8 9  5 7 7 6 4                                          (2,6-dichlorobenzyl-                                                          oxymethyl)tetra-                                                                             1   4  6 9  2 1 6 4 2                                          hydrofuran                                                                    2,5,5-trimethyl-2-(2-                                                                        5   9  9 9  8 7 8 8 8                                          fluorobenzyloxymethyl)-                                                       tetrahydrofuran                                                                              1   4  7 9  7 3 5 8 4                                          2-methyl-2-benzyloxymethyl-                                                                  5   9  7 9  6 7 6 5 3                                          dihydrofuran-5-spiro-                                                         cyclohexane    1   5  2 9  3 1 1 0 0                                          2-methyl-2-benzyloxy-                                                                        5   9  9 9  7 8 7 6 8                                          methyl-tetrahydrofuran-                                                       5-spirocyclohexane                                                                           1   8  8 9  5 5 4 0 1                                          2-methyl-2-(2-methyl-                                                                        5   9  7 9  8 5 7 6 6                                          benzyloxymethyl)-tetra-                                                       hydrofuran-5-spiro-                                                                          1   7  5 9  6 0 6 5 2                                          cyclohexane                                                                   2-methyl-2-(2-fluoro-                                                                        5   9  9 9  8 8 6 6 8                                          benzyloxymethyl)-tetra-                                                       hydrofuran-5-spiro-                                                                          1   7  8 9  6 5 5 6 2                                          cyclohexane                                                                   2-methyl-2-(2,6-dichloro-                                                                    5   8  5 9  6 2 6 6 7                                          benzyloxymethyl)-tetra-                                                       hydrofuran-5-spiro-                                                                          1   8  5 9  5 0 5 6 0                                          cyclohexane                                                                   2,5,5-trimethyl-2-benzyl-                                                                    5   6  8 9  6 2 0 4 0                                          oxymethyl-3,4-epoxy-                                                          tetrahydrofuran                                                                              1   1  2 9  2 0 0 4 0                                          2-ethyl-5,5-dimethyl-2-                                                                      5   9  9 9  9 5 4 4 5                                          benzyloxymethyl-dihydro-                                                      furan          1   8  9 9  7 0 1 2 2                                          2-ethyl-5,5-dimethyl-2-                                                                      5   9  9 9  9 7 6 5 8                                          benzyloxymethyl-tetra-                                                        hydrofuran     1   9  9 9  9 5 4 3 4                                          2-ethyl-5,5-dimethyl-2-                                                                      5   9  9 9  8 8 6 6 8                                          (2,6-dichlorobenzyloxy-                                                       methyl)-tetrahydrofuran                                                                      1   9  9 9  7 6 6 4 3                                          2-ethyl-2-benzyloxy-                                                                         5   9  9 9  6 7 6 5 0                                          methyl-dihydrofuran-                                                          5-spirocyclohexane                                                                           1   9  7 9  4 7 6 7 7                                          2-ethyl-2-(2-fluorobenzyl-                                                                   5                                                              oxymethyl)-tetrahydro-                                                        furan-5-spirocyclohexane                                                                     1   9  7 8  4 7 6 7 7                                          2-ethyl-2-benzyloxymethyl-                                                                   5   9  9 9  7 8 7 4 8                                          tetrahydrofuran-5-spiro-                                                      cyclohexane    1   9  9 9  6 7 6 3 5                                          2-ethyl-2-(2-methylbenzyl-                                                                   5   8  9 9  6 5 5 6 7                                          oxymethyl)-tetrahydro-                                                        furan-5-spirocyclohexane                                                                     1   8  8 9  5 4 5 3 6                                          2-ethyl-2-(2,6-dichloro-                                                                     5   7  3 9  4 6 6 6 2                                          benzyloxymethyl)-tetra-                                                       hydrofuran-5-spiro-                                                                          1   7  2 9  4 4 5 5 1                                          cyclohexane                                                                   2-ethyl-2-(2-bromobenzyl-                                                                    5   7  5 9  4 5 6 4 5                                          oxymethyl)-tetrahydro-                                                        furan-5-spirocyclohexane                                                                     1   7  3 9  4 5 5 4 4                                          2,5,5-trimethyl-4-ethyl-                                                                     5   9  9 9  9 7 5 4 0                                          2-benzyloxymethyl-tetra-                                                      hydrofuran     1   9  7 9  3 4 0 2 0                        __________________________________________________________________________

What we claim is:
 1. A tetrahydrofuran derivative of the formula##STR4## wherein R¹ and R² each individually represents a hydrogen atom,a methyl group, or R¹ and R² together represents a pentamethylenemoiety; R³, R⁴, R⁵, and R⁶ each individually represents a hydrogen atomor one of R³ and R⁴ and one of R⁵ and R⁶ together represent acarbon-carbon bond; R⁷ represents an ethyl group; R⁸ and R⁹ eachindividually represents a hydrogen atom; and Ar represents a phenylgroup or a phenyl group substituted with a 2-methyl-, 2-fluoro- or a2,6-dichloro group. 2.2-Ethyl-5,5-dimethyl-2-benzyloxymethyl-tetrahydrofuran. 3.2-Ethyl-5,5-dimethyl-2-(2,6-dichlorobenzyloxymethyl)-tetrahydrofuran. 4.2-Ethyl-2-benzyloxymethyl-tetrahydrofuran-5-spirocyclohexane. 5.2,5,5-Trimethyl-2-benzyloxymethyl-tetrahydrofuran. 6.2-Ethyl-5,5-dimethyl-2-benzyloxymethyl-dihydrofuran. 7.2-Ethyl-2-benzyloxymethyl-dihydrofuran-5-spirocyclohexane. 8.2,5,5-Trimethyl-4-ethyl-2-benzyloxymethyl-tetrahydrofuran.
 9. Aherbicidal composition comprising as active ingredient a herbicidallyeffective amount of a tetrahydrofuran derivative according to claim 1,and at least one .Iadd.inert .Iaddend.carrier or a surface-active agent.10. A herbicidal composition according to claim 9 wherein thetetrahydrofuran derivative is selected from2-ethyl-5,5-dimethyl-2-benzyloxymethyl-tetrahydrofuran,2-ethyl-5,5-dimethyl-2-(2,6-dichlorobenzyloxymethyl)-tetrahydrofuran,2-ethyl-2-benzyloxymethyl-tetrahydrofuran-5-spirocyclohexane,.Badd..[.2,5,5-trimethyl-2-benzyloxymethyl-tetrahydrofuran,.]..Baddend..Iadd.or.Iaddend.2-ethyl-5,5-dimethyl-2-benzyloxymethyl-dihydrofuran.[.,.]..Iadd.or.Iaddend.2-ethyl-2-benzyloxymethyl-dihydrofuran-5-spirocyclohexane,.Badd..[.2,5,5-trimethyl-4-ethyl-2-benzyloxymethyl-tetrahydrofuran.]..Baddend..11. A method of eradicating or controlling weeds infesting cereal cropsat a locus by applying .Iadd.to the weeds or a locus .Iaddend.aherbicidally .[.active.]. .Iadd.effective .Iaddend.amount of atetrahydrofuran derivative of the formula ##STR5## wherein R¹ and R²each individually represents a hydrogen atom, an alkyl group of up to 6carbon atoms or a phenyl group; or together represent an alkylene moietyof up to 6 carbon atoms; R³, R⁴, R⁵ and R⁶ each individually representsa hydrogen atom, a halogen atom or an alkyl group of up to 6 carbonatoms or one of R³ and R⁴ and one of R⁵ and R⁶ together represent acarbon-carbon bond; R⁷ represents a hydrogen atom or an alkyl group ofup to 6 carbon atoms; R⁸ and R⁹ each individually represents a hydrogenatom or an alkyl group of up to 6 carbon atoms; and Ar represents aphenyl group or a phenyl group substituted by one or more halogen atomsor alkyl or alkoxy groups of up to 6 carbon atoms.
 12. A methodaccording to claim 11, wherein in the tetrahydrofuran derivative R¹ andR² each individually represents a hydrogen atom, methyl group or R¹ andR² together represent a pentamethylene moiety; R³, R⁴, R⁵ and R⁶ eachindividually represents a hydrogen atom or one of R³ and R⁴ and one ofR⁵ and R⁶ together represents a carbon-carbon bond; R⁷ represents ahydrogen atom, a methyl group or an ethyl group; R⁸ and R⁹ eachindividually represents a hydrogen atom; and Ar represents a phenylgroup or a phenyl group substituted with a 2-methyl, 2-fluoro-, or a2,6-dichloro group.
 13. A method according to claim 12 wherein in thetetrahydrofuran derivative R⁷ is an ethyl group.
 14. A method accordingto claim 12 wherein the tetrahydrofuran derivative is selected from2-ethyl-5,5-dimethyl-2-benzyloxymethyl-tetrahydrofuran,2-ethyl-5,5-dimethyl-2-(2,6-dichlorobenzyloxymethyl)-tetrahydrofuran,2-ethyl-2-benzyloxymethyl-tetrahydrofuran-5-spirocyclohexane,2,5,5-trimethyl-2-benzyloxymethyl-tetrahydrofuran,2-ethyl-5,5-dimethyl-2-benzyloxymethyl-dihydrofuran,2-ethyl-2-benzyloxymethyl-dihydrofuran-5-spirocyclohexane,2,5,5-trimethyl-4-ethyl-2-benzyloxymethyl-tetrahydrofuran. .Iadd.
 15. Amethod of controlling plant growth comprises applying to the plant or alocus a herbicidally effective amount of a compound of the formula##STR6## wherein R¹ and R² each individually represents a hydrogen atom,an alkyl group of up to 6 carbon atoms or a phenyl group; or togetherrepresent an alkylene moiety of up to 6 carbon atoms; R³, R⁴, R⁵ and R⁶each individually represent a hydrogen atom, a halogen atom, or an alkylgroup of up to 6 carbon atoms or one of R³ and R⁴ and one of R⁵ and R⁶together represent a carbon-carbon bond; R⁷ represents a hydrogen atomor an alkyl group of up to 6 carbon atoms; R⁸ and R⁹ each individuallyrepresents a hydrogen atom or an alkyl group of up to 6 carbon atoms;and Ar represents a phenyl group or a phenyl group substituted by one ormore halogen atoms or alkyl or alkoxy groups of up to 6 carbon atoms..Iaddend..Iadd.
 16. A method according to claim 15, wherein in thetetrahydrofuran derivative R¹ and R² each individually represents ahydrogen atom, methyl group or R¹ and R² together represent apentamethylene moiety; R³, R⁴, R⁵, and R⁶ each individually represents ahydrogen atom or one of R³ and R⁴ and one of R⁵ and R⁶ togetherrepresents a carbon-carbon bond; R⁷ represents a hydrogen atom, a methylgroup or an ethyl group; R⁸ and R⁹ each individually represents ahydrogen atom; and Ar represents a phenyl group or a phenyl groupsubstituted with a 2-methyl, 2-fluoro-, or a 2,6-dichloro group..Iaddend. .Iadd.
 17. A method according to claim 16 wherein in thetetrahydrofuran derivative R⁷ is an ethyl group. .Iaddend..Iadd.
 18. Amethod according to claim 17 wherein the tetrahydrofuran derivative is2-ethyl-5,5-dimethyl-2-benzyloxymethyl-tetrahydrofuran. .Iaddend..Iadd.19. A method according to claim 17 wherein the tetrahydrofuranderivative is2-ethyl-5,5-dimethyl-2-(2,6-dichlorobenzyloxymethyl)-tetrahydrofuran..Iaddend..Iadd.
 20. A method according to claim 17 wherein thetetrahydrofuran derivative is2-ethyl-2-benzyloxymethyl-tetrahydrofuran-5-spirocyclohexane..Iaddend..Iadd.
 21. A method according to claim 17 wherein thetetrahydrofuran derivative is2-ethyl-5,5-dimethyl-2-benzyloxymethyl-dihydrofuran. .Iaddend..Iadd. 22.A method according to claim 17 wherein the tetrahydrofuran derivative is2-ethyl-2-benzyloxymethyl-dihydrofuran-5-spirocyclohexane..Iaddend..Iadd.
 23. A method according to claim 17 wherein thetetrahydrofuran derivative is2-ethyl-2-(2-fluorobenzyloxymethyl)-tetrahydrofuran-5-spirocyclohexane..Iaddend..Iadd.
 24. A method according to claim 16 wherein thetetrahydrofuran derivative is2-methyl-2-(2-fluorobenzyloxymethyl)-tetrahydrofuran-5-spirocyclohexane..Iaddend..Iadd.
 25. A method according to claim 16 wherein thetetrahydrofuran derivative is2,5,5-trimethyl-2-benzyloxymethyl-tetrahydrofuran. .Iaddend..Iadd.
 26. Amethod according to claim 16 wherein the tetrahydrofuran derivative is2,5,5-trimethyl-4-ethyl-2-benzyloxymethyl-tetrahydrofuran. .Iaddend..Iadd. 27.2-Ethyl-2-(2-fluorobenzyloxymethyl)-tetrahydrofuran-5-spirocyclohexane..Iaddend..Iadd. 28.2-Methyl-2-(2-fluorobenzyloxymethyl)-tetrahydrofuran-5-spirocyclohexane..Iaddend.